Hydrogen sulfide (H2S) and ammonia are commonly found together in process streams produced in commercial processes such as petroleum refining and gasification of carbon-containing materials such as coal, petroleum coke, and heavy oils. Conventionally, the ammonia is removed from gaseous or liquid streams immiscible with water by washing with water and subsequent separation of the phases. Dissolution of the ammonia in the wash water also renders soluble a roughly equimolar amount of hydrogen sulfide. Because of the toxicity of hydrogen sulfide, waste waters containing hydrogen sulfide (“sour water”) must be treated before discharge or reuse. If the liquid stream is to be discharged to public waters, the ammonia must also be removed.
Typically, sour water is treated by distillation to remove both hydrogen sulfide and ammonia as a gaseous mixture. The gas mixture may be further treated in a Claus process, an industry standard for recovery of elemental sulfur. The ammonia in the gas mixture is incinerated in the Claus process to form water and nitrogen gas. Alternatively, sour water may be treated by taking advantage of the fact that the ratio of partial pressure of hydrogen sulfide to the partial pressure of ammonia over water solution increases with increasing temperatures. The sour water is treated under elevated pressure in a two-part distillation process. The first distillation strips out most of the hydrogen sulfide and minor amounts of ammonia as an overhead gas product, which may be further treated with a Claus process. The second distillation produces an overhead gas stream, comprising ammonia with minor amounts of hydrogen sulfide, and a bottoms water stream suitable for discharge or reuse.